Immunohistochemical staining and in situ nucleic acid analysis are tools used in histological diagnosis and the study of tissue morphology. Immunohistochemical staining relies on the specific binding affinity of antibodies with epitopes in tissue samples, and the increasing availability of antibodies which bind specifically with unique epitopes present only in certain types of diseased cellular tissue. Immunohistochemical staining involves a series of treatment steps conducted on a tissue sample (typically a section) mounted on a glass slide to highlight, by selective staining, certain morphological indicators of disease states.
Typical treatment steps include pretreatment of the tissue sample to reduce non-specific binding, antibody treatment and incubation, enzyme labelled secondary antibody treatment and incubation, substrate reaction with the enzyme to produce a fluorophore or chromophore highlighting areas of the tissue sample having epitopes binding with the antibody, counterstaining, and the like. Between each treatment step, the tissue sample must be rinsed to remove unreacted residual reagent from the prior step. Most treatment steps involve a period of incubation typically conducted at ambient temperature of around 25° C. up to around 40° C., while cell conditioning steps are typically conducted at somewhat higher temperatures, e.g. 90° C. to 100° C. In-situ DNA analysis relies upon the specific binding affinity of probes (DNA binding proteins) with unique nucleotide sequences in cell or tissue samples and similarly involves a series of process steps, with a variety of reagents and process temperature requirements. Some specific reactions involve temperatures up to 120° C. to 130° C.
Instrumentation and automated sample processing systems exist for automating some steps in the treatment processes discussed above. However, current systems that involve the use of reaction chambers often result in drying out of tissue samples in between the application of reagents. To compensate, there is a need to constantly hydrate the tissue samples. Automated application of hydration solution to the tissue samples requires use of the robotic reagent dispensation system of the instrument. Because of sample dehydration in automated systems, it is necessary to add extra treatment steps to the process which limits the availability of robotic dispensers for substantive steps required for other reactions being undertaken on the instrument.
Some systems have been designed to reduce sample dehydration by employing a somewhat closed reaction chamber over the slide, into which reagents are introduced. Many of these systems rely on wicking action to draw reagents over the tissue sample. These systems require precise, accurate application of the reagent to a wicking target to ensure consistent and even flow of the reagent into the reaction chamber. If the system loses calibration, application of reagents can miss the wicking target. The adverse effects can be significant and give rise to sample deterioration, wastage of reagent, poor staining, loss of instrument time and delays in sample processing which can have serious implications for patients. To avoid such issues, regular instrument calibration by qualified technicians is required to ensure accurate reagent application, consistent reagent flow and therefore consistent sample staining.
The present invention is aimed at improving upon existing sample staining systems, and/or overcoming or alleviating some of the problems of the prior art.
The discussion of the background to the invention included herein including reference to documents, acts, materials, devices, articles and the like is intended to explain the context of the present invention. This is not to be taken as an admission or a suggestion that any of the material referred to was published, known or part of the common general knowledge as at the priority date of any of the provisional claims.